Concept Guide

IGMP Version 3
Conceptually, IGMP version 3 behaves the same as version 2. However, there are differences.
● Version 3 adds the ability to filter by multicast source, which helps multicast routing protocols avoid forwarding traffic to
subnets where there are no interested receivers.
● To enable filtering, routers must keep track of more state information, that is, the list of sources that must be filtered. An
additional query type, the Group-and-Source-Specific Query, keeps track of state changes, while the Group-Specific and
General queries still refresh the existing state.
● Reporting is more efficient and robust: hosts do not suppress query responses (non-suppression helps track state and
enables the immediate-leave and IGMP snooping features), state-change reports are retransmitted to insure delivery, and a
single membership report bundles multiple statements from a single host, rather than sending an individual packet for each
statement.
The version 3 packet structure is different from version 2 to accommodate these protocol enhancements. Queries are still
sent to the all-systems address 224.0.0.1, as shown in the following illustration, but reports are sent to the all IGMP version
3-capable multicast routers address 244.0.0.22, as shown in the second illustration.
Figure 45. IGMP Version 3 Packet Structure
Figure 46. IGMP Version 3–Capable Multicast Routers Address Structure
Internet Group Management Protocol (IGMP)
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